This invention relates generally to audio/video (A/V) switches and specifically to an interface that provides universal audio/video switching for use with analog and digital television receivers (TVs), video cassette recorders (VCRs) and the like.
Many modern television receivers are microprocessor based with the functions previously performed by analog potentiometers and switches being accomplished electronically. Additionally, a television receiver or an audio/video center may be capable of accepting audio and video signals from a plurality of different sources and providing one or more video outputs for display on a cathode ray tube (CRT) and a single set of stereo audio signals for reproduction by appropriate audio equipment. The video signals may be received from a broadcast receiving antenna, a cable network or from auxiliary devices such as video cassette recorders, video cameras, video disk players, and auxiliary television systems. The various audio inputs may likewise stem from a variety of sources including the above and separate RGB systems and microphone inputs.
A television receiver manufacturer may have a variety of TV receiver models based on different technologies, e.g. analog and digital, and incorporating widely diverse features. One such feature is picture-in-picture (PIP), which enables one or more video display windows to simultaneously display video images different from the main image. This enables a viewer to simultaneously view a given program (the main image) and to monitor one or more other programs displayed in the windows. The PIP feature is provided by undersampling the other video signals which develops a relatively coarse display. As will be seen, one aspect of the invention is to provide an audio/video switching unit capable of interfacing a wide variety of TV receiver models including numerous different features. For example, the interface includes a built in summation circuit for accepting SVHS luma (Y) and SVHS chroma (C) signals and combining them to form a composite video signal (CV) at an output of the interface for application to a PIP processor. Combining the two signals in the interface obviates the need for an additional external analog to digital (A/D) converter to sample the separate Y and C signals. This permits a significant cost reduction and because the wider bandwidth Y and C signals in the SVHS format cannot be utilized effectively in a PIP display, involves no detriment to the viewer. In another TV receiver model, the CV signal provided at the same interface output may be used for a different purpose, e.g. application to a comb filter.
As mentioned above, TV manufacturers often have digital as well as analog receivers in their product lines. It would be desirable to provide a single universal interface, preferably in integrated circuit chip form, for use with such digital and analog systems. The interface would preferably be programmable such that different inputs could selectively be provided at the outputs of the interface, with the signal levels or gains of the output-signals being adjustable, as desired. The programmable gain control amplifiers in the outputs of the interface enable signal level variations to be easily adapted to a variety of end use apparatus.
The interface is designed to be controlled over a three line serial data bus and includes an address decoder, a data decoder (and latch) and a control signal decoder. The control signals control the various electronic switches in the interface for switching the audio and video signals under control of a microprocessor or the like in a television receiver or other control device.
With the system of the invention, a very flexible and economical audio/video signal interface is provided. The interface of the invention may be incorporated in a television receiver or other device or supplied as a stand-alone switching unit that is couplable to such other devices.